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2" visual back?

Zeffer

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Zeffer

Zeffer

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I have just bought MartinBs NS8 GPS :(:D :D :lol:

I was trying to trade my Push fut Lumicon Enhanced Diagonal for a SCT one but with no replies yet. However, I was wondering if I can get a 2" visual back to replace the 1.25" one and then use my Lumicon?

If this is the case is there also a 2" nosepiece with a T-thread so I can keep my camera attached to the nosepiece and just swap the diagonal for the SLR without all the fuss of screwing things on in the dark?

I have searched around but seem to be getting nowhere.

I'd also like to try projection photography using the Baaders so maybe a visual back is the answer for me.

Thanks for any replies in advance!

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moondog

moondog

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Zeffer

I have the same scope. I bought a Williams 2insSCT/ZS66 Adaptor which will take your push fit 2ins diagonal. This is the link to where I bought the Williams adaptor (williams accessories) they also have a cheaper adaptor under the Rigel banner

http://www.iankingimaging.com/

Remember that you will get vignetting with your 2ins diagonal as the hole through the mirror is much less than 2ins.

I have a 2ins T-thread nosepiece which works well with the SCT adaptor. Most suppliers do this size. Ian King have a 2ins nosepiece in accessories

MD

MD

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John

John

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Zeffer

I have the same scope. I bought a Williams 2insSCT/ZS66 Adaptor which will take your push fit 2ins diagonal. This is the link to where I bought the Williams adaptor (williams accessories) they also have a cheaper adaptor under the Rigel banner

http://www.iankingimaging.com/

I use one like the Rigel one above on my C8 very successfully - I did not notice any vignetting when I used 2 inch eyepieces :(

One thing you might want to look out for is to ensure that a 2inch diagonal and the push fit adaptor clear your scope base when pointing towards the zenith - I know the clearence is limited with some designs.

John

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John

John

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From Televue on their 2" SCT diagonal...

"Note that longer focal length 2" eyepieces may vignette severely...."

That may be with a f6.3 reducer attached though..... :( Either way, its something to be aware of. :D

That's interesting. I've used a 2 inch 38mm / 70 degrees FoV eyepiece with my C8 and not had any discernable vignetting - stars seemed bright and clear out to the eyepiece field stop. My 2 inch setup was a Rigel (clone actually) 2 inch push fit visual back (which has a brass compression ring) and an Antares 2 inch mirror diagonal. The eyepiece was a clone of the Rigel 38mm Super Wide Angle.

I worked out that this setup gave me just about the widest possible field I could get with my C8 - a 1.32 degree true field, and the field stop of the eyepiece was certainly bigger than the rear aperture of the OTA - so why didn't I see vignetting ??? - perhaps certain combinations / eyepiece designs suffer more from it than others ?. Maybe it was there but is a more subtle effect than I was looking for ?.

The one noticable disadvantage I did have with the setup was the weight of the EP / visual back / 2 inch diagonal was quite considerable and upset the balance of my C8 which was a 10 year old fork mounted one.

John

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moondog

moondog

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With the 2ins adaptor on the C8 @ F10 and using the Moonfish 2ins diagonal and Moonfish 30mm WA I could see some vignetting.

John - Michael Swanson's book on the C8 says that @ F10 the max True FOV with a 2ins EP is 1 deg. At F6.3 (with reducer) the max True FOV is 1.3 deg.

MD

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John

John

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With the 2ins adaptor on the C8 @ F10 and using the Moonfish 2ins diagonal and Moonfish 30mm WA I could see some vignetting.

John - Michael Swanson's book on the C8 says that @ F10 the max True FOV with a 2ins EP is 1 deg. At F6.3 (with reducer) the max True FOV is 1.3 deg.

MD

Thanks MD.

I calculated my FoV by dividing the FoV of the eyepiece (70 degrees in this case) by the power it gives in the scope (52.6x in a C8 working at F10). The result I got was 1.33 degrees as a true field. Maybe Swanson was taking vignetting caused by the size of the aperture at the back of the OTA into account in his figure or maybe I'm not using the right calculation (quite possible :().

John

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moondog

moondog

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For a C11 the True Field of View with a 2ins eyepiece is given as 1 deg in the Michael Swanson book. This is the same as the C8.

With a 1 1/4 ins EP the True FOV for the C8 is 0.9 deg and the C11 is 0.6 deg.

The C11 therefore must have a larger hole in its mirror.

Think of the hole in the mirror as being the field stop of an EP.

MD

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Zeffer

Zeffer

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Thanks for all the help here. I have gone for the Rigel one and expect it tomorrow. I'm not sure I even know what vignetting is. Would it look as if I were looking down a toilet tube or something?

When I had the Celestron 2" diagonal and 40mm Axiom EP I had no trouble at all, but maybe that's irrelevant (steep learning curve this hobby).

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